Much effort has been made to reinforce metals with fibers that are sufficiently refractory to withstand the temperatures needed to make and use such composites.
Ceramic, or refractory oxide, fibers in the form of whiskers have been suggested as a means of enhancing the high temperature strength of metals. However, composites containing the desired high volume of aligned and uniformly distrubuted whiskers in the metal matrix have not been obtained because the small single crystalline whiskers are difficult to handle.
The use of continuous fibers would alleviate the problems encountered with short fibers but it has been difficult to prevent breakage of such fibers and damage to their surfaces. Such breakage and surface damage weaken the reinforcement capabilities of continuous fibers. In addition, the common continuous filament refractory fibers, carbon fibers and boron fibers oxidize at elevated temperatures, causing a decrease in their strengthening capabilities.
Long fibers of single crystal alumina are known. However, due to the large diameters (about 10 mils) of these fibers and their smooth surfaces, they pull out and separate causing the composite to fail in use and during machining.
Moreover, many combinations of fibers and metals give poor composites due to excessive reaction between the fiber and the metal which causes the formation of a brittle phase and deterioration of properties.
In addition, the bonding between the metal and the fibers necessary for strength of composites made heretofore has been found to deteriorate generally on heating of the composite, resulting in a significant loss of properties. This may be due, in the instance of infiltration of fibers by molten metal, to the inability of the molten metal to wet the fibers sufficiently to cause good bonding between them or to excessive fiber-metal reaction.
It is an object of this invention to provide a metal composite that substantially obviates the above problems.